The present invention relates generally to data communications. More particularly, the present invention relates to automatic gain control for orthogonal frequency-division multiplexing (OFDM) receivers in local area network (LAN) systems.
In OFDM wireless LANs (WLANs) such as those specified by IEEE Standard 802.11a, 802.11g, and 802.11n, data is transmitted in bursts of variable duration that are separated by inter-burst gaps of fixed duration. FIG. 1 shows a conventional OFDM WLAN signal 100 comprising a plurality of bursts 102A-K separated by inter-burst gaps (ISG) 103. Each burst 102 comprises a plurality of preamble fields 106A,B-N, each followed by a respective signal field 108A,B-N and a respective payload field 110A,B-N each comprising a packet of data 112A,B-N.
Payload fields 110 comprise packets 112 of variable length, and so are of variable duration, generally on the order of ten or 100 microseconds. In contrast, preamble fields 106 are used by the receiver of signal 100 to acquire signal 100, and so must have a predetermined minimum duration on the order of tens of microseconds. Therefore, in many cases, preambles 106 constitute the majority of the bandwidth of signal 100.